Method and system for determining an optimum drive signal for an acoustic transducer

ABSTRACT

A method and system is disclosed for determining an optimum drive signal for an acoustic transducer. A pulse signal is employed as a wideband reference signal Vr(t); and, in a pulse-echo measurement a corresponding wideband echo signal Ve(t) is obtained. A normalized loop frequency response {circumflex over (X)}(f) for the acoustic transducer is defined as a ratio of a Fourier Transform of the Ve(t) to a Fourier Transform of the Vr(t), and a normalized loop time response X(t) is defined as an Inverse Fourier Transform of the {circumflex over (X)}(f). An optimum drive signal B(t) for the acoustic transducer is defined as B(t)α*G(t), wherein a coefficient α is determined to multiply a function G(t), in which the function G(t) is derived from one of the normalized loop time response X(t) and the normalized loop frequency response {circumflex over (X)}(f).

BACKGROUND Technical Field

The present invention relates to a method and system for determining anoptimum drive signal on energy efficiency basis for an acoustictransducer in an acoustic probe.

Description of Related Art

An acoustic transducer is a key component in an acoustic imaging system.The technologies of acoustic imaging have been frequently employed tonon-destructive testing, clinical diagnosis, and under waterapplications due to such advantages of acoustic imaging as non-invasive,non-ionization, real-time imaging, and cost-effectiveness. For example,acoustic imaging for clinical diagnosis, which is used for assessing thesoft tissue structure and blood flow, is currently the most usedclinical imaging modality after conventional X-ray radiography.

FIG. 1A and FIG. 1B show a typical structure of an acoustic probe. Anacoustic probe 113 has a transducer array 117A which comprises aplurality of acoustic transducer 117. The number of acoustic transducer117 in the transducer array 117A is greater than or equal to one.

In the prior art, a sensitivity is used to assess the characteristics ofan acoustic transducer 117. FIGS. 2A˜2B show the method of sensitivitymeasurement for an acoustic transducer in an acoustic probe in a priorart. FIG. 2A shows a measuring arrangement for reference signal in aprior art. A sine burst generator 200 is arranged to output a sine burstsignal at a specific frequency on an external 50-ohm load as a referencesignal V_(r)(t) 204. FIG. 2B shows a measuring arrangement for anacoustic probe 113 in a prior art. The sine burst generator of 200 iselectrically coupled to an acoustic probe 113 which is immersed in awater bath 208 with an acoustic mirror 212. The acoustic probe 113 isdriven by the sine burst generator 200 and transmit an acoustic sineburst wave 214 at the specific frequency. The acoustic probe 113receives the reflected sine burst wave 218 from the acoustic mirror 212and outputs an echo signal V_(e)(t) 224.

FIG. 3A shows a reference signal for an acoustic probe in a prior art.The reference signal V_(r)(t) 204 is a sine burst signal with aminimum-run of 15 cycles at a specific frequency; and, a peak-to-peakvoltage of reference signal (V_(ppr)) is obtained. FIG. 3B shows an echosignal for an acoustic probe in a prior art. The echo signal V_(e)(t)224 is a sine burst signal at the specific frequency; and a peak-to-peakvoltage of echo signal (V_(ppe)) is obtained. A loop sensitivity for theacoustic transducer is calculated based upon the peak-to-peak voltage ofecho signal (V_(ppe)) to the peak-to-peak voltage of reference signal(V_(ppr)).

The disadvantage for the prior art is that one specific frequency isadopted for measuring a loop sensitivity of an acoustic transducer 117in an acoustic probe 113. In an early stage, traditional acoustic proberesponds to narrow band frequency only. However, wideband acoustic probehas been developed due to rapid progress in the acoustic technologydevelopment in recent years. Therefore, there is a general need for amethod and system for measuring wideband characteristics of an acoustictransducer such as normalized loop time response X(t) and optimum drivesignal on energy efficiency basis.

SUMMARY

The present invention discloses a method and system for measuringwideband characteristics of an acoustic transducer in an acoustic probe;the wideband characteristics include normalized loop time response X(t)and optimum drive signal B(t) on energy efficiency basis.

A method for determining an optimum drive signal for an acoustictransducer in an acoustic probe is introduced according to the presentinvention.

A pulse generator of 50-ohm source impedance, which is used to generateunipolar pulse and bipolar pulse, electrically couples to an external50-ohm load to obtain a wideband reference signal V_(r)(t) on the 50-ohmload and further obtain a function {circumflex over (V)}_(r)(f) that isa Fourier Transform of the wideband reference signal V_(r)(t).

In a first and second embodiments, the adopted pulse is a negative-goingunipolar pulse and positive-going unipolar pulse, respectively; and in athird and fourth embodiments, the adopted pulse is a negative-positivebipolar pulse and positive-negative bipolar pulse, respectively.

The pulse generator of 50-ohm source impedance electrically couples toan acoustic probe for measuring the wideband characteristics of anacoustic transducer. The acoustic probe is immersed into a water bathwith an acoustic mirror. The acoustic probe is aligned so that theacoustic wave is normally incident to and reflected from the acousticmirror. An acoustic transducer in the acoustic probe is driven by thepulse generator of 50-ohm source impedance and transmit a widebandacoustic wave toward the acoustic mirror. The transmitted widebandacoustic wave travels and reaches the acoustic mirror and is reflectedbackward to the acoustic transducer in the water bath. The acoustictransducer receives the reflected wideband acoustic wave and outputs awideband echo signal V_(e)(t); and, a function {circumflex over(V)}_(e)(f) that is a Fourier Transform of the wideband echo signalV_(e)(t) is obtained.

A normalized loop frequency response {circumflex over (X)}(f) of theacoustic transducer is defined as the ratio of the function {circumflexover (V)}_(e)(f) to the function {circumflex over (V)}_(r)(f); that is,

${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}},$

according to the present invention.

A normalized loop time response X(t) for the acoustic transducer isdefined as an Inverse Fourier Transform of the normalized loop frequencyresponse {circumflex over (X)}(f); that is,

X(t)

Inverse Fourier Transform of the {circumflex over (X)}(f),

according to the present invention.

The normalized loop frequency response {circumflex over (X)}(f) and thenormalized loop time response X(t) for the acoustic transducer arestored in one of a firmware and a program memory according to thepresent invention.

An optimum drive signal B(t) for an acoustic transducer is defined asB(t)

α*G(t), wherein a coefficient a is determined to multiply a functionG(t); and, the function G(t) is derived from one of the normalized looptime response X(t) and the normalized loop frequency response{circumflex over (X)}(f), according to the present invention.

The function G(t) is obtained as a self-deconvolution of the normalizedloop time response X(t); that is,

G(t)=self-deconvolution of the X(t),

according to the present invention.

As well, the function G(t) is calculated as an Inverse Fourier Transformof a square root of the normalized loop frequency response {circumflexover (X)}(f), that is,

G(t)=Inverse Fourier Transform of the √{square root over ({circumflexover (X)}(f))},

according to the present invention.

The function G(t) is stored in one of the firmware and the programmemory according to the present invention.

The drive signal B(t) is stored in a programmable waveform generator forgenerating an optimum drive signal for driving the acoustic transduceraccording to the present invention.

The measuring method for determining the optimum drive signal B(t) isembedded in one of the firmware and the program memory according to thepresent invention.

A system for determining and generating an optimum drive signal for anacoustic transducer in an acoustic probe is introduced according to thepresent invention. The system comprises a pulse generator, a signalprocessing unit, a transducer selector, a programmable waveformgenerator, and a control unit. The control unit further comprises afirmware, a program memory, and a storage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A˜1B show a typical structure for an acoustic probe in a priorart.

FIG. 2A shows a measuring arrangement for reference signal in a priorart.

FIG. 2B shows a measuring arrangement for an acoustic probe in a priorart.

FIG. 3A shows a reference signal for an acoustic probe in a prior art.

FIG. 3B shows an echo signal for an acoustic probe in a prior art.

FIGS. 4A˜4B show a negative-going unipolar pulse used as a widebandreference signal and its energy spectrum for a first embodimentaccording to the present invention.

FIGS. 5A˜5B show a positive-going unipolar pulse used as a widebandreference signal and its energy spectrum for a second embodimentaccording to the present invention.

FIG. 6A shows a typical energy spectrum of wideband reference signalbased on a unipolar pulse signal for a first and second embodimentsaccording to the present invention.

FIG. 6B shows a typical frequency response for an acoustic transducer inthe first and second embodiments according to the present invention.

FIGS. 7A˜7B show a negative-positive bipolar pulse used as a widebandreference signal and its energy spectrum for a third embodimentaccording to the present invention.

FIGS. 8A˜8B show a positive-negative bipolar pulse used as a widebandreference signal and its energy spectrum for a fourth embodimentaccording to the present invention.

FIG. 9A shows a typical energy spectrum of wideband reference signalbased on a bipolar pulse signal for the third and fourth embodimentsaccording to the present invention.

FIG. 9B shows a typical frequency response for an acoustic transducer inthe third and fourth embodiments according to the present invention.

FIG. 10A shows a measuring arrangement for a wideband reference signalaccording to the present invention.

FIG. 10B shows a measuring arrangement for an acoustic probe accordingto the present invention.

FIG. 11A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on anegative-going unipolar pulse for a first embodiment.

FIG. 11B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thenegative-going unipolar pulse for the first embodiment.

FIG. 12A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on apositive-going unipolar pulse for a second embodiment.

FIG. 12B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thepositive-going unipolar pulse for the second embodiment.

FIG. 13A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on afirst bipolar pulse for a third embodiment.

FIG. 13B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the firstbipolar pulse for the third embodiment.

FIG. 14A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on asecond bipolar pulse for a fourth embodiment.

FIG. 14B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the secondbipolar pulse for the fourth embodiment.

FIG. 15 shows a flow chart for determining an optimum drive signal foran acoustic transducer according to the present invention.

FIG. 16A shows a measured normalized loop time response for a givenacoustic transducer according to the present invention.

FIG. 16B shows an optimum drive signal based on the measured normalizedloop time response for the given acoustic transducer according to thepresent invention.

FIG. 17 shows a system for determining and generating an optimum drivesignal for an acoustic transducer in an acoustic probe according to thepresent invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention discloses a method and system for measuringwideband characteristics of an acoustic transducer in an acoustic probe;the wideband characteristics include normalized loop time response X(t)and optimum drive signal on energy efficiency basis. The “loop” meansthe pulse-echo mode in which an acoustic transducer transmits anacoustic wave out and a corresponding reflected echo wave is received bythe same acoustic transducer.

A method and system for determining an optimum drive signal on energyefficiency basis for an acoustic transducer in an acoustic probe isintroduced according to the present invention.

A pulse signal is adopted as a wideband reference signal V_(r)(t) formeasuring wideband characteristics of an acoustic transducer accordingto the present invention. There are four embodiments of adopted pulsesignal used in the present invention, which include a negative-goingunipolar pulse 400 for a first embodiment, a positive-going unipolarpulse 500 for a second embodiment, a negative-positive bipolar pulse 700for a third embodiment, and a positive-negative bipolar pulse 800 for afourth embodiment, according to the present invention.

FIGS. 4A˜4B show a negative-going unipolar pulse used as a widebandreference signal and its energy spectrum for a first embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of negative-going unipolar pulse 400 is adopted in the firstembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of negative-going unipolar pulse 404is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofnegative-going unipolar pulse 400.

FIGS. 5A˜5B show a positive-going unipolar pulse used as a widebandreference signal and its energy spectrum for a second embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of positive-going unipolar pulse 500 is adopted in the secondembodiment, and an energy spectrum of wideband reference signal1/50{circumflex over (V)}_(r)(f)|² of positive-going unipolar pulse 504is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofpositive-going unipolar pulse 500.

FIG. 6A shows a typical energy spectrum of wideband reference signalbased on a unipolar pulse signal for the first and second embodimentsaccording to the present invention. A maximum energy spectrum density ofthe energy spectrum of wideband reference signal 404, 504 is at 0 Hz(f₀). An upper bound frequency (f₄) of the energy spectrum of widebandreference signal 404, 504 is a frequency where the energy spectrumdensity drops down to a certain decibel value (e.g., −6 dB) relative tothe maximum energy spectrum density at 0 Hz (f₀).

FIG. 6B shows a typical frequency response for an acoustic transducer inthe first and second embodiments according to the present invention. Amaximum frequency response of an acoustic transducer is usually at itscentral frequency or resonant frequency. The upper bound frequency (f₃)and lower bound frequency (f₂) for the frequency response of acoustictransducer 600 are frequencies where the frequency response drops downto a certain decibel value (e.g., −6 dB) relative to its maximumresponse located at between (f₂) and (f₃), respectively.

To assure a good signal-to-noise ratio for the measurement in the firstand second embodiments, the requirement is that the upper boundfrequency (f₄) of the energy spectrum of wideband reference signal 404,504 is greater than the upper bound frequency (f₃) of the frequencyresponse of the acoustic transducer 600, that is, f₄>f₃, according tothe present invention.

FIGS. 7A˜7B show a negative-positive bipolar pulse used as a widebandreference signal and its energy spectrum for a third embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of negative-positive bipolar pulse 700 is adopted in the thirdembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of negative-positive bipolar pulse704 is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofnegative-positive bipolar pulse 700.

FIGS. 8A˜8B show a positive-negative bipolar pulse used as a widebandreference signal and its energy spectrum for a fourth embodimentaccording to the present invention. The wideband reference signalV_(r)(t) of positive-negative bipolar pulse 800 is adopted in the fourthembodiment, and an energy spectrum of wideband reference signal1/50|{circumflex over (V)}_(r)(f)|² of positive-negative bipolar pulse804 is obtained, in which the function {circumflex over (V)}_(r)(f) is aFourier Transform of the wideband reference signal V_(r)(t) ofpositive-negative bipolar pulse 800.

FIG. 9A shows a typical energy spectrum of wideband reference signalbased on a bipolar pulse signal for the third and fourth embodimentsaccording to the present invention. The lower bound frequency (f₁) andupper bound frequency (f₄) of the energy spectrum of wideband referencesignal 704, 804 are frequencies where the energy spectrum density dropsdown to a certain decibel value (e.g., −6 dB) relative to its maximumlocated at between (f₁) and (f₄), respectively.

FIG. 9B shows a typical frequency response for an acoustic transducer inthe third and fourth embodiments according to the present invention. Amaximum frequency response for the acoustic transducer is usually at itscentral frequency or resonant frequency. The upper bound frequency (f₃)and lower bound frequency (f₂) for the frequency response of acoustictransducer 900 are frequencies where the frequency response drops downto a certain decibel value (e.g., −6 dB) relative to its maximumresponse located at between (f₂) and (f₃), respectively.

To assure a good signal-to-noise ratio for the measurement in the thirdand fourth embodiments, the requirement is that the upper boundfrequency (f₄) of the energy spectrum of wideband reference signal 704,804 is greater than the upper bound frequency (f₃) of the frequencyresponse of the acoustic transducer 900 and the lower bound frequency(f₁) of the energy spectrum of wideband reference signal 704, 804 issmaller than the lower bound frequency (f₂) of the frequency response ofthe acoustic transducer 900; that is, f₄>f₃>f₂>f₁, according to thepresent invention.

FIG. 10A shows a measuring arrangement for a wideband reference signalaccording to the present invention. An external 50-ohm load iselectrically coupled to a pulse generator of 50-ohm source impedance1000 that generates unipolar pulse and bipolar pulse to obtain awideband reference signal V_(r)(t) 400, 500, 700, 800 on the 50-ohmload.

FIG. 10B shows a measuring arrangement for an acoustic probe accordingto the present invention. The pulse generator of 50-ohm source impedance1000 electrically couples to an acoustic probe 113 for measuring thewideband characteristics of an acoustic transducer 117. The acousticprobe 113 is immersed into a water bath 208 with an acoustic mirror 212.The acoustic probe 113 is aligned so that the acoustic wave is normallyincident to and reflected from the acoustic mirror 212. An acoustictransducer 117 in the acoustic probe 113 is driven by the pulsegenerator of 50-ohm source impedance 1000 and transmit a widebandacoustic wave toward the acoustic mirror 212. The transmitted widebandacoustic wave 1004 travels and reaches the acoustic mirror 212 in thewater bath 208 and is reflected backward to the acoustic transducer 117.The acoustic transducer 117 receives the reflected wideband acousticwave 1008 and outputs a wideband echo signal V_(e)(t) 1100, 1200, 1300,1400.

FIG. 11A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on anegative-going unipolar pulse for a first embodiment. The widebandreference signal V_(t)(t) of negative-going unipolar pulse 400 isadopted in the first embodiment and a function {circumflex over(V)}_(r)(f), that is a Fourier Transform of the wideband referencesignal V_(r)(t) of negative-going unipolar pulse 400, is obtained.Meanwhile, an energy of reference signal (E_(r)) for wideband referencesignal V_(r)(t) of negative-going unipolar pulse 400 is calculated asone of a time-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,

E _(r)=1/50∫V _(r)(t)² dt=1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 11B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thenegative-going unipolar pulse for the first embodiment. A wideband echosignal V_(e)(t) based on negative-going unipolar pulse 1100 is obtainedin the first embodiment and a function {circumflex over (V)}_(e)(f),that is a Fourier Transform of the wideband echo signal V_(e)(t) basedon negative-going unipolar pulse 1100, is further obtained. Meanwhile,an energy of echo signal (E_(e)) for wideband echo signal V_(e)(t) basedon negative-going unipolar pulse 1100 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is, E_(e)=1/50∫V_(e)(t)²dt=1/50∫|{circumflex over(V)}_(e)(f)|²df.

FIG. 12A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on apositive-going unipolar pulse for a second embodiment. The widebandreference signal V_(r)(t) of positive-going unipolar pulse 500 isadopted in the second embodiment and a function {circumflex over(V)}_(r)(f), that is a Fourier Transform of the wideband referencesignal V_(r)(t) of positive-going unipolar pulse 500, is obtained.Meanwhile, an energy of reference signal (E_(r)) for wideband referencesignal V_(r)(t) of positive-going unipolar pulse 500 is calculated asone of a time-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,

E _(r)=1/50∫V _(r)(t)² dt=1/50 ∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 12B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on thepositive-going unipolar pulse for the second embodiment. A wideband echosignal V_(e)(t) based on positive-going unipolar pulse 1200 is obtainedin the second embodiment and a function {circumflex over (V)}_(e)(f),that is a Fourier Transform of the wideband echo signal V_(e)(t) basedon positive-going unipolar pulse 1200, is further obtained. Meanwhile,an energy of echo signal (E_(e)) for wideband echo signal V_(e)(t) basedon positive-going unipolar pulse 1200 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,

E _(e)=1/50∫V _(e)(t)² dt=1/50∫|{circumflex over (V)} _(e)(f)|² df.

FIG. 13A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on afirst bipolar pulse for a third embodiment. The wideband referencesignal V_(r)(t) of negative-positive bipolar pulse 700 is adopted in thethird embodiment and a function {circumflex over (V)}_(r)(f), that is aFourier Transform of the wideband reference signal V_(r)(t) ofnegative-positive bipolar pulse 700, is obtained. Meanwhile, an energyof reference signal (E_(r)) for wideband reference signal V_(r)(t) ofnegative-positive bipolar pulse 700 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,

E _(r)=1/50∫V _(r)(t)² dt=1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 13B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the firstbipolar pulse for the third embodiment. A wideband echo signal V_(e)(t)based on negative-positive bipolar pulse 1300 is obtained in the thirdembodiment and a function {circumflex over (V)}_(e)(f), that is aFourier Transform of the wideband echo signal V_(e)(t) based onnegative-positive bipolar pulse 1300, is further obtained. Meanwhile, anenergy of echo signal (E_(e)) for wideband echo signal V_(e)(t) based onnegative-positive bipolar pulse 1300 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,

E _(e)=1/50∫V _(e)(t)² dt=1/50∫|{circumflex over (V)} _(e)(f)|² df.

FIG. 14A shows an electrical waveform of a wideband reference signal andits Fourier Transform according to the present invention based on asecond bipolar pulse for a fourth embodiment. The wideband referencesignal V_(r)(t) of positive-negative bipolar pulse 800 is adopted in thefourth embodiment and a function {circumflex over (V)}_(r)(f), that is aFourier Transform of the wideband reference signal V_(r)(t) ofpositive-negative bipolar pulse 800, is obtained. Meanwhile, an energyof reference signal (E_(r)) for wideband reference signal V_(r)(t) ofpositive-negative bipolar pulse 800 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband referencesignal; that is,

E _(r)=1/50∫V _(r)(t)² dt=1/50∫|{circumflex over (V)} _(r)(f)|² df.

FIG. 14B shows an electrical waveform of a wideband echo signal and itsFourier Transform according to the present invention based on the secondbipolar pulse for the fourth embodiment. A wideband echo signal V_(e)(t)based on positive-negative bipolar pulse 1400 is obtained in the fourthembodiment and a function {circumflex over (V)}_(e)(f), that is aFourier Transform of the wideband echo signal V_(e)(t) based onpositive-negative bipolar pulse 1400, is further obtained. Meanwhile, anenergy of echo signal (E_(e)) for wideband echo signal V_(e)(t) based onpositive-negative bipolar pulse 1400 is calculated as one of atime-integral of the power of wideband reference signal and afrequency-integral of the energy spectrum density of wideband echosignal; that is,

E _(e)=1/50∫V _(e)(t)² dt=1/50∫|{circumflex over (V)} _(e)(f)|² df.

A normalized loop frequency response {circumflex over (X)}(f) for theacoustic transducer is defined as a ratio of the function {circumflexover (V)}_(e)(f) which is a Fourier Transform of the wideband echosignal V_(e)(t) to the function {circumflex over (V)}_(r)(f) which is aFourier Transform of the wideband reference signal V_(r)(t); that is,

${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}},$

according to the present invention.

A normalized loop time response X(t) for the acoustic transducer isdefined as an Inverse Fourier Transform of the normalized loop frequencyresponse {circumflex over (X)}(f); that is,

X(t)

Inverse Fourier Transform of the {circumflex over (X)}(f),

according to the present invention.

An optimum drive signal B(t) for an acoustic transducer is defined asB(t)

α*G(t), wherein a coefficient a is determined to multiply a functionG(t); and, the function G(t) is derived from one of the normalized looptime response X(t) and the normalized loop frequency response{circumflex over (X)}(f), according to the present invention.

The function G(t) is obtained as a self-deconvolution of the normalizedloop time response X(t); that is,

G(t)=self-deconvolution of the X(t),

according to the present invention.

As well, the function G(t) is calculated as an Inverse Fourier Transformof a square root of the normalized loop frequency response {circumflexover (X)}(f), that is,

G(t)=Inverse Fourier Transform of the √{square root over ({circumflexover (X)}(f))},

according to the present invention.

FIG. 15 shows a flow chart for determining an optimum drive signal foran acoustic transducer according to the present invention.

The measuring step for defining a normalized loop frequency response{circumflex over (X)}(f) and a normalized loop time response X(t)comprises:

-   -   preparing a pulse generator and a signal processing unit;    -   generating a pulse to create a wideband signal as a reference        signal;    -   obtaining a wideband reference signal V_(r)(t);    -   obtaining a function {circumflex over (V)}_(r)(f) that is a        Fourier Transform of the wideband reference signal V_(r)(t);    -   storing the function {circumflex over (V)}(f) that is a Fourier        Transform of the wideband reference signal V_(r)(t) in one of a        firmware and a program memory;    -   coupling the pulse generator and the signal processing unit to        an acoustic transducer;    -   generating a wideband acoustic wave from the acoustic        transducer;    -   obtaining a wideband echo signal V_(e)(t) after the acoustic        wave being reflected from an acoustic mirror;    -   obtaining a function {circumflex over (V)}_(e)(f) that is a        Fourier Transform of the wideband echo signal V_(e)(t);    -   defining a normalized loop frequency response {circumflex over        (X)}(f) as follows:

{circumflex over (X)}(f)

{circumflex over (V)}_(e)(f)/{circumflex over (V)}_(r)(f);

-   -   defining a normalized loop time response X(t) as follows:

X(t)

Inverse Fourier Transform of the {circumflex over (X)}(f); and

-   -   storing the normalized loop frequency response {circumflex over        (X)}(f) and the normalized loop time response X(t) in one of the        firmware and the program memory.

The pulse is one of a unipolar pulse and a bipolar pulse. The unipolarpulse is one of a negative-going pulse 400 and a positive-going pulse500. The bipolar pulse is one of a negative-positive bipolar pulse 700and a positive-negative bipolar pulse 800.

The measuring step for obtaining a function G(t) from one of thenormalized loop frequency response {circumflex over (X)}(f) and thenormalized loop time response X(t) comprises:

-   -   calculating a function G(t) as an Inverse Fourier Transform of a        square root of the normalized loop frequency response        {circumflex over (X)}(f):        -   G(t)=Inverse Fourier Transform of the √{square root over            ({circumflex over (X)}(f))};    -   obtaining a function G(t) as a self-deconvolution of the        normalized loop time response X(t):        -   G(t)=self-deconvolution of the X(t); and    -   storing the function G(t) in one of the firmware and the program        memory.

The measuring step for determining an optimum drive signal B(t) for theacoustic transducer comprises:

-   -   obtaining the function G(t);    -   defining a drive signal B(t) for the acoustic transducer as        follows:

B(t)

α*G(t), wherein

-   -   -   a coefficient α is determined to multiply the function G(t);

    -   storing the drive signal B(t) in one of the firmware and the        program memory; and

    -   storing the drive signal B(t) in a programmable waveform        generator, wherein the drive signal B(t) is an optimum drive        signal on energy efficiency basis for the acoustic transducer.

An example of measuring a normalized loop time response X(t) anddetermining an optimum drive signal B(t) for an acoustic transducer inan acoustic probe was performed according to the present invention, andthe results are shown in FIG. 16. FIG. 16A shows a measured normalizedloop time response for a given acoustic transducer, and FIG. 16B showsan optimum drive signal based on the measured normalized loop timeresponse for the given acoustic transducer.

The acoustic transducer under test in the example is in a transducerarray of a commercial acoustic probe containing one hundred andninety-two (192) acoustic transducers. The central frequency andbandwidth of the transducer are 7.3 MHz and 80%, respectively. In themeasurement, a negative-going unipolar pulse with an amplitude of −75volts and an upper bound frequency of 55 MHz was adopted as a widebandreference signal. The distance between the acoustic transducer andacoustic mirror is 20 mm. And, the material of the acoustic mirror isstainless-steel with an acoustic reflection coefficient of 0.93 in awater bath.

FIG. 17 shows a system for determining and generating an optimum drivesignal for an acoustic transducer in an acoustic probe according to thepresent invention.

The system 1700 comprises a pulse generator 1701, a programmablewaveform generator 1703, a signal processing unit 1702, a transducerselector 1704, and a control unit 1706. The control unit 1706 furthercomprises a firmware 1707, a program memory 1708, and a storage 1709.

The control unit 1706 is electrically coupled to the pulse generator1701, to the programmable waveform generator 1703, to the signalprocessing unit 1702, and to external output devices 1730.

The pulse generator 1701 is electrically coupled to an acoustictransducer through the transducer selector 1704 for generating a pulseto create a wideband acoustic wave from the acoustic transducer. Thepulse is one of a unipolar pulse and a bipolar pulse. The unipolar pulseis one of a negative-going pulse 400 and a positive-going pulse 500. Thebipolar pulse is one of a negative-positive bipolar pulse 700 and apositive-negative bipolar pulse 800.

The reflected wideband echo wave is received by the acoustic transducerthrough the transducer selector 1704 to the signal processing unit 1702for further processing. The transducer selector 1704 sequentially orrandomly selects one transducer of a transducer array in an acousticprobe 113.

The measuring method for obtaining the normalized loop frequencyresponse {circumflex over (X)}(f) and normalized loop time response X(t)is embedded in one of the firmware 1707 and the program memory 1708according to the present invention.

The measuring method for obtaining the function G(t) from normalizedloop frequency response {circumflex over (X)}(f) is embedded in one ofthe firmware 1707 and the program memory 1708 according to the presentinvention.

The measuring method for obtaining the function G(t) from the normalizedloop frequency response {circumflex over (X)}(f) is embedded in one ofthe firmware 1707 and the program memory 1708 according to the presentinvention.

The measuring method for determining the optimum drive signal B(t) forthe acoustic transducer is embedded in one of the firmware 1707 and theprogram memory 1708 according to the present invention. The optimumdrive signal B(t) is further stored in the programmable waveformgenerator 1703 for generating an optimum drive signal for driving theacoustic transducer according to the present invention.

All data of measurement are stored in the storage 1709 and output to theoutput devices 1730 according to the present invention.

While several embodiments have been described by way of example, it willbe apparent to those skilled in the art that various modifications maybe configured without departing from the spirit of the presentinvention. Such modifications are all within the scope of the presentinvention, as defined by the appended claims.

Numerical system  113 acoustic probe  117A transducer array  117acoustic transducer  200 sine burst generator  204 reference signal  208water bath  212 acoustic mirror  214 transmitted acoustic sine burstwave  218 reflected sine burst wave  224 echo signal  400 widebandreference signal of negative-going unipolar pulse  404 energy spectrumof wideband reference signal of negative-going unipolar pulse  500wideband reference signal of positive-going unipolar pulse  504 energyspectrum of wideband reference signal of positive-going unipolar pulse 600 frequency response of acoustic transducer  700 wideband referencesignal of negative-positive bipolar pulse  704 energy spectrum ofwideband reference signal of negative-positive bipolar pulse  800wideband reference signal of positive-negative bipolar pulse  804 energyspectrum of wideband reference signal of positive-negative bipolar pulse 900 frequency response of acoustic transducer 1000 pulse generator 1004transmitted wideband acoustic wave 1008 reflected wideband acoustic wave1100 wideband echo signal based on negative-going unipolar pulse 1200wideband echo signal based on positive-going unipolar pulse 1300wideband echo signal based on negative-positive bipolar pulse 1400wideband echo signal based on positive-negative bipolar pulse 1608optimum drive signal 1700 system 1701 pulse generator 1702 signalprocessing unit 1703 programmable waveform generator 1704 transducerselector 1706 control unit 1707 firmware 1708 program memory 1709storage 1730 output devices

NOTATION Reference Signal

(V_(ppr)) peak-to-peak voltage of reference signal (E_(r)) energy ofreference signal;$E_{r} = {{\frac{1}{50}{\int{{V_{r}(t)}^{2}{dt}}}} = {\frac{1}{50}{\int{{{{\hat{V}}_{r}(f)}}^{2}{df}}}}}$(BW_(r)) bandwidth of reference signal; (D_(r))${{energy}\mspace{14mu} {density}\mspace{14mu} {of}\mspace{14mu} {reference}\mspace{14mu} {signal}};{D_{r} = \frac{E_{r}}{{BW}_{r}}}$V_(r)(t) wideband reference signal; {circumflex over (V)}_(r)(f) FourierTransform of the wideband reference signal V_(r)(t);$\frac{1}{50}{{{\hat{V}}_{r}(f)}}^{2}$ energy spectrum of widebandreference signal;

Echo Signal

(V_(ppe)) peak-to-peak voltage of echo signal; (E_(e))${{energy}\mspace{14mu} {of}\mspace{14mu} {echo}\mspace{14mu} {signal}};{E_{e} = {{\frac{1}{50}{\int{{V_{e}(t)}^{2}{dt}}}} = {\frac{1}{50}{\int{{{{\hat{V}}_{e}(f)}}^{2}{df}}}}}}$(BW_(e)) bandwidth of echo signal; (D_(e))${{energy}\mspace{14mu} {density}\mspace{14mu} {of}\mspace{14mu} {echo}\mspace{14mu} {signal}};{D_{e} = \frac{E_{e}}{{BW}_{e}}}$V_(e)(t) wideband echo signal; {circumflex over (V)}_(e)(f) FourierTransform of the wideband echo signal V_(e)(t);$\frac{1}{50}{{{\hat{V}}_{e}(f)}}^{2}$ energy spectrum of widebandecho signal;

Definition

{circumflex over (X)}(f)${{{normalized}\mspace{14mu} {loop}\mspace{14mu} {frequency}\mspace{14mu} {response}\mspace{20mu} {\hat{X}(f)}}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}};{{\hat{X}(f)}\overset{def}{=}{{{\hat{V}}_{e}(f)}\text{/}{{\hat{V}}_{r}(f)}}};${circumflex over (V)}_(e)(f)/{circumflex over (V)}_(r)(f); X(t)normalized loop time response; Inverse Fourier Transform of the{circumflex over (X)}(f)${X(t)}\overset{def}{=}{{Inverse}\mspace{14mu} {Fourier}\mspace{14mu} {Transform}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} {\hat{X}(f)}}$S_(L)(f) wideband loop sensitivity is defined as an absolute square ofthe {circumflex over (X)}(f) in${decibel};{{S_{L}(f)}\overset{def}{=}{10\mspace{11mu} \log {{\hat{X}(f)}}^{2}}}$(S_(LC))${{characteristic}\mspace{14mu} {loop}\mspace{14mu} {sensitivity}\mspace{14mu} S_{LC}}\overset{def}{=}{10\mspace{11mu} \log \; \left( \frac{D_{e}}{D_{r}} \right)}$G(t)${{Inverse}\mspace{14mu} {Fourier}\mspace{14mu} {Transform}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} \sqrt{\hat{X}(f)}};$${{G(t)} = {{Inverse}\mspace{14mu} {Fourier}\mspace{14mu} {Transform}\mspace{14mu} {of}\mspace{14mu} {the}\mspace{14mu} \sqrt{\hat{X}(f)}}}\mspace{14mu}$self-deconvolution of the X(t); G(t) = Self-deconvolution of the X(t)B(t) an optimum drive signal on energy efficiency basis for the acoustictransducer; $\begin{matrix}{{{B(t)}\overset{def}{=}{\alpha*{G(t)}}},{{wherein}\mspace{14mu} a\mspace{14mu} {coefficient}\mspace{14mu} \alpha \mspace{14mu} {is}\mspace{14mu} {determined}\mspace{14mu} {to}\mspace{14mu} {multiply}\mspace{14mu} {the}}} \\{{function}\mspace{14mu} {{G(t)}.}}\end{matrix}\quad$

What is claimed is:
 1. A method for determining an optimum drive signalfor an acoustic transducer, the measuring step comprising: generating apulse to create a wideband signal as a reference signal; obtaining awideband reference signal V_(r)(t); obtaining a function {circumflexover (V)}_(r)(f) that is a Fourier Transform of the wideband referencesignal V_(r)(t); generating a wideband acoustic wave from the acoustictransducer; obtaining a wideband echo signal V_(e)(t) after the acousticwave being reflected from an acoustic mirror; obtaining a function{circumflex over (V)}_(e)(f) that is a Fourier Transform of the widebandecho signal V_(e)(t); defining a normalized loop frequency response{circumflex over (X)}(f):${{\hat{X}(f)}\overset{def}{=}\frac{{\hat{V}}_{e}(f)}{{\hat{V}}_{r}(f)}},$and defining a normalized loop time response X(t): X(t)

Inverse Fourier Transform of the {circumflex over (X)}(f).
 2. A methodfor determining an optimum drive signal for an acoustic transducer asclaimed in claim 1, the measuring step further comprising: calculating afunction G(t) as a self-deconvolution of the normalized loop timeresponse X(t);
 3. A method for determining an optimum drive signal foran acoustic transducer as claimed in claim 1, the measuring step furthercomprising: calculating a function G(t) as an Inverse Fourier Transformof a square root of the normalized loop frequency response {circumflexover (X)}(f).
 4. A method for determining an optimum drive signal for anacoustic transducer as claimed in claim 2, the measuring step furthercomprising: defining a drive signal B(t) for the acoustic transducer:B(t)

α*G(t), wherein a coefficient α is determined to multiply the functionG(t).
 5. A method for determining an optimum drive signal for anacoustic transducer as claimed in claim 3, the measuring step furthercomprising: defining a drive signal B(t) for the acoustic transducer:B(t)

α*G(t), wherein a coefficient α is determined to multiply the functionG(t).
 6. A method for determining an optimum drive signal for anacoustic transducer as claimed in claim 1, wherein the pulse is one of aunipolar pulse and a bipolar pulse.
 7. A method for determining anoptimum drive signal for an acoustic transducer as claimed in claim 6,wherein the unipolar pulse is one of a negative-going pulse and apositive-going pulse.
 8. A method for determining an optimum drivesignal for an acoustic transducer as claimed in claim 6, wherein thebipolar pulse is a negative-going pulse first and a positive-going pulsesecond.
 9. A method for determining an optimum drive signal for anacoustic transducer as claimed in claim 6, wherein the bipolar pulse isa positive-going pulse first and a negative-going pulse second.
 10. Amethod for determining an optimum drive signal for an acoustictransducer as claimed in claim 2, further comprising: storing thefunction G(t) in one of a firmware and a program memory.
 11. A methodfor determining an optimum drive signal for an acoustic transducer asclaimed in claim 3, further comprising: storing the function G(t) in oneof a firmware and a program memory.
 12. A method for determining anoptimum drive signal for an acoustic transducer as claimed in claim 4,further comprising: storing the drive signal B(t) in one of a firmwareand a program memory.
 13. A method for determining an optimum drivesignal for an acoustic transducer as claimed in claim 5, furthercomprising: storing the drive signal B(t) in one of a firmware and aprogram memory.
 14. A system for determining an optimum drive signal foran acoustic transducer, comprises: a pulse generator electricallycoupled to an acoustic transducer for generating a pulse to create awideband acoustic wave; a programmable waveform generator electricallycoupled to the acoustic transducer for generating a drive signal todrive the acoustic transducer; and a control unit electrically coupledto the pulse generator and the programmable waveform generator.
 15. Asystem for determining an optimum drive signal for an acoustictransducer as claimed in claim 14, wherein the control unit furthercomprising a firmware and a program memory.